So you use a laptop backpack to protect your valuable (and expensive) tech from knocks and bumps. Don't stop there—protect your pack and its contents from downpours with the Sea To Summit Ultra-Sil Pack Cover. The Sea to Summit pack cover is a lightweight and weather resistant pack cover that does a good job in keeping the pack dry. It weighs less than 100 grams, and easily pops unnoticed inside your backpack in its own tiny stuff sack.